I have tried 30 Hz on my 4K monitors and that doesn't work either. Even if it did work, 30 Hz would be basically unacceptable. But it doesn't work for me, so the point is moot.

The Surface Book, apparently unlike the Surface Pro 4, partially obscures its internal mini-DisplayPort port by the dock connector. So I cannot use the internal port when the dock is attached. I have (not yet, at least) shaved down the plastic of any of my mini-DP cables to attempt to fabricate one compatible with the limited space afforded by the dock cable.

I apologize ahead of time for those who are disinterested in 4K monitor support for the Surface Book, but I have further news to report here. Based on the article I linked in the above message, I went to the relatively extreme length of filing down one of my DisplayPort cables so that the mini-DP side had no plastic sheath, allowing it to fit (snugly) alongside the Surface Dock connector:

Unfortunately, this does not work on the Surface Book, which is a variation versus the Surface Pro 4. When the dock connector is connected, the base-connected monitor is powered off. It is powered on if the dock connector is disconnected.

So even with this approach, the Surface Book only powers a single 4K monitor at a time. Very disappointing.

Keying off of the sentiment raised by BearFlag concerning the drivers, is there a consensus forming about whether the Surface dock will ever support two 4K monitors as was promised?

I've got all of the latest firmware updates and the latest Windows 10 build installed (non-Insider, mind you) and the dock still does not work with two 4K monitors attached.

As I have posted above, this is further frustrated by the fact that the Surface Book's engineering made the built-in mini DisplayPort difficult to reach with a conventional mDP cable when the dock is attached. However, with some shaving of cable connectors, it is possible to attach a mDP cable to the Surface Book base while the dock connector is attached. Nevertheless, this does not resolve the problem and the inability to power two 4K monitors remains.

I'd really like to hear from anyone else who has two 4K monitors: is there any magic incantation to get this to work? Frankly, I'd like Microsoft to explain how they felt comfortable making the advertised claim that this supports two 4K monitors. Certainly somewhere at Microsoft (in a QA lab perhaps?) this was set up for testing? How was it done?

I suppose this appears to have evolved/devolved into my own crusade for dual 4K monitor support with the Surface Book and dock, but I do have some optimism to share. Today, I was connected with a Surface Support representative that did two things I've been looking for:

Acknowledged the issue was known by the Surface Support team and Microsoft.

It is being worked on.

Relatively simple matters, I suppose, but these mean a lot to this particular user. They give me reason to keep waiting.

In fact, the representative optimistically says a fix is in the pipeline, though I would not personally keep anyone to such a timeline. In fact, knowing it is being worked on and a fix will arrive "soon" is sufficient. If it arrives later this month, in mid December, or at the end of the year, ultimately any of these are fine by me. I can wait a reasonable amount of time. I just want to use my second monitor soon.

I apologize ahead of time for those who are disinterested in 4K monitor support for the Surface Book, but I have further news to report here. Based on the article I linked in the above message, I went to the relatively extreme length of filing down one of my DisplayPort cables so that the mini-DP side had no plastic sheath, allowing it to fit (snugly) alongside the Surface Dock connector:

Unfortunately, this does not work on the Surface Book, which is a variation versus the Surface Pro 4. When the dock connector is connected, the base-connected monitor is powered off. It is powered on if the dock connector is disconnected.

So even with this approach, the Surface Book only powers a single 4K monitor at a time. Very disappointing.

Click to expand...

If they designed it to not have enough space for both cables to be connected at the same time, that must be their way of passively saying it doesn't work.
They certainly can't expect Surface Book owners to shave the cables to get them connected.

If they designed it to not have enough space for both cables to be connected at the same time, that must be their way of passively saying it doesn't work.
They certainly can't expect Surface Book owners to shave the cables to get them connected.

Click to expand...

That sure is the default reasonable point of view, especially if we give the designers the benefit of the doubt of not accidentally putting the port too close to the dock connector port. But multiple people had suggested the (remote) possibility that maybe a second 4K monitor could be powered if it were possible to connect one of the two monitors to the base, thereby only using one of the two connectors in the Surface Dock. Such a configuration would ostensibly avoid the dock's apparent inability to power two 4K monitors simultaneously.

Of course, that doesn't actually work, and few would be surprised it doesn't work. But it was a fairly easy matter to modify one of my multitude of DisplayPort cables and test it out, and I'm glad that I've confirmed the hunch that it wouldn't work. If I had not done the test and on some crazy chance someone later confirmed that it did work, I would be disappointed to have been needlessly waiting to use my second 4K monitor.

As it is, I feel comfortable that I have done everything reasonable and within my power to get the advertised dual 4K monitor functionality to work and have determined it simply does not work. Now I have confirmation Microsoft is aware and working on it. This is good news, if merely a small bite of good news for now.

Any update, protip? I don't have two 4k monitors now but I may one day and I'm curious to know if it's possible as well.

At work, every time I plug in my SB to the new dock I have to go through a 5 minute song and dance just to get it to work. I haven't been to work in a few weeks now and I'm hoping the drivers are updated before I go back but are you able to just use a single 4k monitor at 60hz just by connecting the dock? Does yours throw a fit as well?

Displayport 1.2 link is limited to a single 4k monitor at 60 Hz. Driving Multiple Displays from a Single DisplayPort Output - DisplayPort
That is why the important point is how many links are coming out of the connector. If it is only a single DP 1.2 link, then it cannot drive two 4k at 60 Hz, period. If it is two DP 1.2 links then it should be able to drive both 4k at 60 Hz. But a Skylake only has three available video outputs. Assume one to the internal panel, one to the side port and one to the dock/power port and you have the three available video outputs. So that means while the dock may have two miniDP ports, their configuration is unclear but most likely there is an internal MST hub, which means a single DP 1.2 and thus only one 4k at 60 Hz.

You should try to run one 4k from the dock and one directly from the Book miniDP port. That is your best bet for getting to two 4k at 60 Hz, if they are indeed two different links from the Skylake. That is a much better chance than trying them from the dock alone.

On my SPro3, I had to connect the MST and the two 4k 30 Hz to the side miniDP port. The SPro3 dock port was too flaky.

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FYI:

I tried connecting to Surface Book while connected to the SB Dock connector. It blocks the DisplayPort jack on the side, which might be for a reason.

But with that said, this is on the MS website concerning the multiple monitor setup at the following: Connect Surface to a TV, monitor, or projector. There is also a Snip-it of the chart attached in this post. So (2) 60hz 4k at max 2560 x 1600 can work on all Surface Books.

I have a Dell P2715Q Ultra HD 3840 x 2160 resolution, and my other monitor is FHD 1080p, 1920 x 1080. The Surface Book does not struggle at all but cannot support a second monitor in Ultra UHD resolution. Also, the Dell monitor needs to be set up a certain way on the OSD to achieve 60hz and since it is new is assuredly a DP 1.2 cable. Hope this helps.

Attached Files:

Any update, protip? I don't have two 4k monitors now but I may one day and I'm curious to know if it's possible as well.

At work, every time I plug in my SB to the new dock I have to go through a 5 minute song and dance just to get it to work. I haven't been to work in a few weeks now and I'm hoping the drivers are updated before I go back but are you able to just use a single 4k monitor at 60hz just by connecting the dock? Does yours throw a fit as well?

Click to expand...

I can say that I just tried with the newest available build of Windows 10, including all the appropriate drivers on any refresh rate (60/30) setting, and I am still unable to drive two external 4K monitors of any type. It doesn't matter if I use DP 2.2 or HDMI etc...

Any update, protip? I don't have two 4k monitors now but I may one day and I'm curious to know if it's possible as well.

Click to expand...

On the Surface dock, no update. I have at this point given up on attempting to drive two 4K monitors at 60 Hz with the Surface Book + dock. I believe it's simply not possible given these pieces of hardware. There have been some creative workarounds suggested elsewhere such as using a USB display adapter, but I have not tried that.

In the meantime, I've replaced my Surface Book + dock with a normal desktop workstation. I had been experimenting with the Book in a role of a mobile-capable workstation (which would be used 90% of the time in a docked configuration), but that hasn't panned out due to this apparent hardware limitation. But modern desktop workstations have absolutely no problem driving multiple 4K monitors.

(I still have the Surface Book, but I'll no longer be using the dock.)